1. Field of the Invention
The present invention relates to a speed or gear-changing mechanism that can be operated while a device is either in a kinetic or a static condition. More specifically, the invention relates to a speed or gear changing mechanism in which a plurality of paired gears having different gear ratios are employed in a relatively simple construction that has particular application in relatively light power transmitting circumstances such as a drive arrangement in a bicycle.
2. Description of Related Art
Speed changing mechanisms currently used in bicycles are a specific area in which the complexity of the mechanisms lead to serious drawbacks in operation, maintenance, the cost of the original equipment, and the repair and replacement of components. The more popular touring, mountain, and racing bicycles employ multiple-speed gearing and shifting mechanisms, including sixteen speed, twenty-one speed, and even twenty-four speed mechanisms, that almost universally employ both front and rear derailleurs. The front and rear derailleurs are employed to change between generally two or three front drive gears and generally seven or eight rear driven gears. The drive gears and driven gears are coupled by a single drive chain that engages one front and one rear sprocket gear at any given time, and the drive chain must be physically moved by the derailleurs to other sprocket gears when changing speeds.
Speed-change mechanisms based upon the use of derailleurs involve the use of many component parts, and have proven to be very sensitive, both in the area of properly operating the shift levers to obtain the desired drive-to-driven gear ratio, and in the area of maintenance of the system, including the adjustment of the shift levers, cabling and positioning of the derailleur components that engage the drive chain to move it between adjacent gears. Shift indexers have been employed in an attempt to avoid the common problem of the bicycle rider overshifting or undershifting, wherein the transition of the drive chain from a current position to engagement with a different desired gear is not effected smoothly and on a first attempt. However, shift indexers add to the overall complexity of the system, and must rely on the proper positioning, during initial assembly and after any subsequent reassembly, of the front and rear derailleurs and their installation on the bicycle. Further, the tightened tolerances in an indexed system make it very difficult for non-experts to perform any maintenance or repair work on the speed changing system.
A further disadvantage of derailleur-based speed changing mechanisms is that the gear ratio between the drive and driven gears can be changed only while the bicycle is in motion, thus preventing a speed change in a stopped or static condition. At this juncture, it may be helpful to note that the gear ratios are usually not specifically referred to as such, rather, those gear ratios are responsible for effecting changes in the "gear" (e.g., first gear, second gear, and so on). The term "speed" is also used in the context of the bicycle having sixteen, twenty-one, or twenty-four "speeds". With the ever-increasing use of bicycles in recreational uses, and by less experienced riders, the ability to change speeds while stationary is seen as being highly advantageous. Along the same lines, the need for a highly reliable and accurate mechanism that will repeatedly effect the speed changes desired, without the sort of trial and error involved in moving shift levers in a derailleur-based system to obtain the desired gear ratio, is of increasing importance.
The ability to more readily customize a speed changing mechanism to provide a desired set of specific gear ratios or speeds on a rider-by-rider basis is also desirable, given the wide range of riding experience, physical condition, and general athletic ability encountered in the bicycle-riding community. This capability is likely to be limited in derailleur-based systems, in that adjacent gears in the drive gear set and adjacent gears in the driven gear set generally have to be relatively close in size to allow the drive chain to be easily moved from one gear to the next.
An additional drawback of current derailleur-based speed changing mechanisms is in the shift mechanism employed to effect the selection of a desired speed. In the systems employing both front and rear derailleurs, two separate shift levers are used, and frequently are designed and installed on the bicycle such that shifting to a smaller sprocket on both the front and rear derailleur involves moving the shift levers in the same direction. However, moving to a smaller sprocket on the front derailleur has the opposite effect (decreasing drive ratio) of moving to a smaller sprocket on the rear derailleur (increasing drive ratio). This shift pattern can cause confusion to the rider in determining what shifting action needs to be effected in order to bring about the desired speed change. It is also often difficult for the rider to remember whether the "speed" currently in use involves engagement of one of the exterior sprockets on the front or rear gearset. Particularly in view of the fact that it is possible to shift the drive chain completely off of a front or rear gearset in a derailleur system, thereby disengaging the chain and disabling the drive mechanism, the complexity of the shift pattern is a significant problem.
Speed changing mechanisms that avoid the use of derailleurs have previously been disclosed in the art, including the mechanism shown in U.S. Pat. No. 4,813,302, issued to the inventor in the present application. That speed change mechanism avoids entirely the use of a drive chain coupling a drive gear to a driven gear in propelling the bicycle. Two variations on another mechanism that employs the use of two pairs of sprocket gears having each gear pair coupled by a dedicated sprocket chain are disclosed in two U.S. patents (U.S. Pat. No. 528,954 and U.S. Pat. No. 528,856) issued to Lippy et al. The design of those systems, including the shifting and gear pair engagement or clutch mechanisms, effectively limit those devices to use in providing two available speeds to the bicycle rider. At the present time, there is little, if no, use for a speed changing mechanism of the type disclosed in these Lippy et al. patents, as those provide only two different speeds, and there are currently available much more effective and reliable three-speed shifting mechanisms in which only a single drive chain is used, and the gear ratio change is effected internally in the hub of the rear wheel of the bicycle. Even with the relative simplicity, reliability and availability of three-speed changers, the overwhelming demand among bicyclists aged from the early teens through adulthood is for bicycles that provide a number of different speeds in excess of three, and generally no less than five different speeds.
The use of a gear train including a plurality of spur gear pairs selectable by the shifting of an intermediate gear to mesh with a desired gear pair has also been proposed. Such all-gear transmissions or power trains are inefficient as compared to sprocket gear and sprocket chain systems, and thus are generally undesirable for use on bicycles, as there are few, if any, advantages provided by all-gear systems, and the extra work required to achieve the same level of power output is a serious disadvantage, given that the work must be provided by the bicycle rider.
It is therefore a principal object of the present invention to provide a speed changing mechanism for a bicycle that avoids the use of a derailleur or derailleurs and the moving of a drive chain from sprocket to sprocket in order to change speeds or shift gears.
It is also an important object of the present invention to provide a speed changing mechanism that requires a minimal amount of maintenance, is capable of allowing the rider to shift gears both in dynamic and static modes, and which readily permits custom selection of gear pairs of different gear ratios to achieve the desired bicycle drive ratios suitable for a particular rider.